Mechanical control cables of the push-pull type are well known. They typically comprise a cable enclosed by a somewhat flexible supporting housing that allows for a transfer of motion around curves by the cable. The housing also provides mechanical protection to the cable, minimizing the risk of mechanical damage to the cable and maintaining the cable in a cleaner condition than if it were exposed.
Typical supporting housings are of helically wound metal wire, commonly of a flat wire that allows the inner surface of the housing to be relatively smooth. The supporting housing generally extends for the length of the cable system with the cable exposed only at the ends of the supporting housing. Both single and multiple strand cables are used. The cables are preferably lubricated to reduce operating friction and extend the life of the system. The lubricant is subject to contamination, including dirt, moisture, salt and sweat, at the system ends where the cable is exposed. Operation of the system results in contamination being carried into the housing, eventually causing increased friction, corrosion, wear and ultimately stretching or breakage of the cable. Frequent maintenance is necessary to avoid these problems, particularly if the system is routinely operated in dirty environments. Maintenance requires disassembly, cleaning, lubrication and reassembly.
Flexible supporting housings are often fitted with flexible polymeric tubular liners to reduce operating friction and maintenance. Additionally the cable may also be provided with a polymeric covering for the same reasons.
Cable systems for high performance applications such as bicycles are desired to have a minimal amount of weight. For these applications, it is known to use flexible supporting housings, preferably with a flexible polymeric tubular liner, only on the substantially curved portions of the systems so that the substantially straight portion comprises only an exposed portion of the cable. While offering significantly reduced weight, these types of systems suffer from increased contamination because of having a greater length of cable exposed to the environment.